The aim of the present study was to evaluate the clinical features of childhood-onset Familial Mediterranean fever (FMF) patients and to assess the phenotype-genotype correlation. The study included patients with childhood-onset FMF that followed up over a period of 18 years in the Division of Pediatric Allergy and Immunology clinic. Twelve MEFV mutations were investigated in all patients. The patients were classified into four groups according to mutations: 1, M694V homozygote; 2, M694V heterozygote; 3, compound heterozygote for M694V; and 4, other-other gene mutation group. The following parameters were evaluated: gender, age of onset, age at diagnosis, time interval between disease onset and diagnosis, fever, abdominal pain, chest pain, arthralgia, arthritis, myalgia, vomiting, diarrhea, constipation, headache, erysipela-like erythema, protracted febrile myalgia, splenomegaly, hepatomegaly, consanguinity, number of attacks before and after treatment, severity score, response to colchicine treatment. Of the 124 patients included in the study, 105 had at least one MEFV gene mutation. M694V homozygosity was the most common mutation, followed by M694V heterozygotes and M694V-M680I compound heterozygotes. Severity score was found significantly higher in patients with M694V homozygote and compound heterozygote for M694V compared with other groups. The data supported the findings in literature that FMF patients with M694V homozygote and compound heterozygote for M694V gene mutations experience a more severe clinical course.